1. Field of the Invention
This invention relates to a reproducing apparatus and more particularly to a reproducing apparatus arranged to be capable of generating a clock signal synchronized in phase with reproduced data.
2. Description of Related Art
The reproducing apparatuses of the above-stated kind include digital VTRs which are arranged to record and reproduce video signals in the form of digital signals on and from magnetic tapes. The digital VTRs are being developed not only for broadcasting stations but also for home use. The home-use digital VTRs obtain video images mainly from TV broadcast. However, other sources of video images have come to be often used, including the analog VTRs of VHS and 8-mm systems, personal computers, TV games, etc.
In extracting a clock signal from a data train being received by an apparatus which transmits data at a high speed, such as a digital VTR, it is known to use a phase-locked loop (hereinafter referred to as PLL) which is arranged as shown in FIG. 1.
Referring to FIG. 1, a phase difference between reproduced data and a clock signal is detected by a phase comparison circuit 701. A low-pass filter (hereinafter referred to as LPF) 702 filters a signal indicative of the phase difference thus obtained by the phase comparison circuit 701, and the filtered signal is supplied to a voltage-controlled oscillator (hereinafter referred to as VCO) 703 as a control signal. The VCO 703 generates a clock signal having a frequency corresponding to the voltage of the control signal. A frequency divider 704 then frequency-divides the clock signal outputted from the VCO 703 and feeds the frequency-divided clock signal back to the phase comparison circuit 701.
However, in all the apparatuses mentioned above, PLL circuits employed for generating a clock signal are configured as analog circuits. The analog circuits are apt to have their characteristics vary with variations of ambient conditions such as temperature, aging, etc., and thus result in an unstable clock signal generating action.
Meanwhile, the digital VTRs are also required, like in the case of analog VTRs, to have special reproducing functions such as fast feeding, slow reproduction, etc. However, in carrying out such a special reproducing function, the relative speed of a head to a tape vary to cause variations in frequency of the reproduced signal. If the frequency of the reproduced signal varies too much, the frequency comes out of the lock range of the PLL, thereby making it impossible to obtain an adequate clock signal.
Further, for obtaining more appropriate data, the digital VTR is provided with an equalizer for equalizing the waveform of the reproduced signal. However, if the equalizing characteristic of the equalizer is fixedly set to obtain an optimum waveform for normal reproduction, the amount of errors in reproduced data increases to deteriorate picture quality in the event of a special reproduction, since the frequency of the reproduced signal varies during the special reproduction, as mentioned above, and the set characteristic is not appropriate for the special reproduction.
Further, the video signals obtained from the video image sources of varied kinds mentioned above sometimes have variations of time base to such a degree that the video signals are hardly considered to be standard signals. However, the frequency variable ranges of crystal oscillators hitherto used for digital VTRs as recording operation clock signal generating circuits have been too narrow for processing the input video signals of varied kinds mentioned above. This problem may be solved by providing an additional VCO for recording. However, the provision of the additional VCO results in an increase in the number of parts and is, therefore, against a desired reduction in cost and size.